Latex is an aqueous suspension of hydrocarbon polymer. When the suspended hydrocarbon polymer is coagulated using an acid or (as is more commonly used) calcium nitrate, the coagulated material drops out of the aqueous phase as a solid. This solid can be of a single latex type, or it can be a combination of latex-type polymers. The hydrocarbon polymer(s) suspended in the aqueous phase can be selected to provide a specific formulated blend. When the latex is natural (derived from plant sources), a natural rubber product is produced. When the latex is synthetic (artificially produced using emulsion polymerization techniques), a synthetic rubber product is produced. For example, when chloroprene monomers (2-chloro-1,3-butadiene) are polymerized (reacted to link into a chain), the resulting product is known as polychloroprene or chloroprene rubber, more commonly known by the trade name Neoprene, which is available from DuPont Performance Elastomers L.L.C. of Wilmington, Del., USA.
Naturally-occurring ozone gas is corrosive to natural rubber and causes it to degrade, thereby compromising the integrity of devices in which natural rubber is a component. Some synthetic rubbers, on the other hand, exhibit a resistance to ozone that is superior in comparison to natural rubber. Unfortunately, many synthetic rubbers and most notably the highly ozone resistant chloroprene-based rubbers are currently significantly higher in cost than natural rubber. To increase ozone resistance to a rubber product, polychloroprene latex is blended with natural latex in the compound formulation stage at a blend ratio level to impart the ozone resistance of the polychloroprene to the overall material. The higher the polychloroprene ratio to natural latex, the higher ozone resistance will be.
To facilitate effective ozone resistance at a cost that is more reasonable given the cost of chloroprene rubber, rubber that is a mixture of chloroprene rubber and natural rubber has been derived. To produce a very minimal ozone-resistant compound, the chloroprene content is typically about 30% by weight (wt. %). This 30% chloroprene content is only marginally better than natural rubber alone. About 40% polychloroprene is needed to cause a substantial increase in ozone resistance to be realized. At 40%, there is a sufficient saturation of polychloroprene to cover the natural rubber particles and to provide suitable resistance to ozone degradation. The combination of natural rubber and chloroprene rubber at the proper ratio thus allows the benefits of both materials to be realized. More specifically, by blending the natural and chloroprene rubbers, ozone resistance from the polychloroprene is realized, and elasticity, strength, and tear resistance from the natural rubber is realized. However, the high cost of polychloroprene makes it a less than optimum material for use in rubber products, particularly at the levels currently used.
What is needed is a more cost-effective material that can be used in conjunction with polychloroprene to provide suitable ozone resistance to rubber.